The spermatogenesis and oogenesis-specific helix-loop-helix transcription factor 2 (Sohlh2) is exclusively expressed in germ cells of male and female gonad. Sohlh2 acts as a transcriptional factor via its specific DNA binding site, E-box to regulate target genes such as Lhx8, Zp genes, Ngn3. Sohlh2 localize in the female oocyte and in the male spermatogonia. However, the regulatory mechanism of Sohlh2 was poorly understood. In this study, we examine the patterns interacting with Sohlh2. First, we performed immunoprecipitation with the antibody against Sohlh2 protein extracts from the testis. Two-dimensional SDS-gel showed sexual distinguishable protein including Fkbp12, 13, 3, 59. Among them, Fkbp3 is a member of the immunophilin protein family, which play a role in immunoregulation and basic cellular processes involving protein folding and trafficking. Protein is a cis-trans prolyl isomerase that binds the immunosuppressants FK506 and rapamycin. It has a higher affinity for rapamycin than for FK506 and thus may be an important target molecule for immunosuppression by rapamycin. In the expression analysis of Fkbp3 is detected in the multiple tissues; intestine, stomach, kidney, spleen, liver, heart, brain, lung, uterus, ovary, testis. Here, we identified that Fkbp3 mRNA is detected in the ovary and testis, kidney, liver, heart, brain, lung. Immunostaning assay shows that Fkbp3 is localized at the spermatogonia in testis. In further studies, in order to confirm the interaction between Fkbp3 and Sohlh2, we will perform immunoprecipitation.